C++ 迭代时从向量中删除项目？
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Removing item from vector while iterating?
提问by Lucas
I have a vector that holds items that are either active or inactive. I want the size of this vector to stay small for performance issues, so I want items that have been marked inactive to be erased from the vector. I tried doing this while iterating but I am getting the error "vector iterators incompatible".
我有一个包含活动或非活动项目的向量。我希望此向量的大小保持较小以解决性能问题，因此我希望从向量中删除已标记为非活动的项目。我在迭代时尝试这样做，但我收到错误“向量迭代器不兼容”。
vector<Orb>::iterator i = orbsList.begin();
while(i != orbsList.end()) {
bool isActive = (*i).active;
if(!isActive) {
orbsList.erase(i++);
}
else {
// do something with *i
++i;
}
}
回答by Moo-Juice
The most readable way I've done this in the past is to use std::vector::erasecombined with std::remove_if. In the example below, I use this combination to remove any number less than 10 from a vector.
我过去做过的最易读的方法是std::vector::erase结合使用std::remove_if. 在下面的示例中，我使用此组合从向量中删除任何小于 10 的数字。
(For non-c++0x, you can just replace the lambda below with your own predicate:)
（对于非的C ++ 0x，只需更换下面与您自己的谓词拉姆达：）
// a list of ints
int myInts[] = {1, 7, 8, 4, 5, 10, 15, 22, 50. 29};
std::vector v(myInts, myInts + sizeof(myInts) / sizeof(int));
// get rid of anything < 10
v.erase(std::remove_if(v.begin(), v.end(),
[](int i) { return i < 10; }), v.end());
回答by Vassilis
I agree with wilx's answer. Here is an implementation:
我同意威尔克斯的回答。这是一个实现：
// curFiles is: vector < string > curFiles;
vector< string >::iterator it = curFiles.begin();
while(it != curFiles.end()) {
if(aConditionIsMet) {
it = curFiles.erase(it);
}
else ++it;
}
回答by wilx
You can do that but you will have to reshuffle your while()a bit, I think. The erase()function returns an iterator to the element next after the erased one: iterator erase(iterator position);. Quoting from the standard from 23.1.1/7:
你可以这样做，但while()我认为你必须重新洗牌。该erase()函数返回一个迭代器到被擦除元素之后的下一个元素：iterator erase(iterator position);。引用自 23.1.1/7 的标准：
The iterator returned from a.erase(q) points to the element immediately following q prior to the element being erased. If no such element exists, a.end() is returned.
从 a.erase(q) 返回的迭代器指向在元素被擦除之前紧跟在 q 之后的元素。如果不存在这样的元素，则返回 a.end()。
Though maybe you should be using the Erase-remove idiominstead.
虽然也许您应该改用Erase-remove 成语。
回答by Pierre
erasereturns a pointer to the next iterator value (same as Vassilis):
erase返回指向下一个迭代器值的指针（与 Vassilis 相同）：
vector <cMyClass>::iterator mit
for(mit = myVec.begin(); mit != myVec.end(); )
{ if(condition)
mit = myVec.erase(mit);
else
mit++;
}
回答by Dawid Drozd
If someone need working on indexes
如果有人需要处理索引
vector<int> vector;
for(int i=0;i<10;++i)vector.push_back(i);
int size = vector.size();
for (int i = 0; i < size; ++i)
{
assert(i > -1 && i < (int)vector.size());
if(vector[i] % 3 == 0)
{
printf("Removing %d, %d\n",vector[i],i);
vector.erase(vector.begin() + i);
}
if (size != (int)vector.size())
{
--i;
size = vector.size();
printf("Go back %d\n",size);
}
}
回答by Raedwald
You might want to consider using a std::listinstead of a std::vectorfor your data structure. It is safer (less bug prone) to use when combining erasure with iteration.
您可能要考虑对数据结构使用 astd::list而不是 a std::vector。将擦除与迭代结合使用时，使用起来更安全（不易出错）。
回答by Maxim Egorushkin
As they said, vector's iterators get invalidated on vector::erase()no matter which form of iterator increment you use. Use an integer index instead.
正如他们所说，vector::erase()无论您使用哪种形式的迭代器增量，vector 的迭代器都会失效。改用整数索引。
回答by Oliver Charlesworth
Removing items from the middle of a vector will invalidate all iterators to that vector, so you cannot do this (update: without resorting to Wilx's suggestion).
从向量中间删除项目将使该向量的所有迭代器无效，因此您不能这样做（更新：不求助于威尔克斯的建议）。
Also, if you're worried about performance, erasing items from the middle of a vector is a bad idea anyway. Perhaps you want to use an std::list?
此外，如果您担心性能，从向量中间擦除项目无论如何都是个坏主意。也许您想使用std::list?
